Sensorless position estimation of simulated direct driven hydraulic actuators

This study researched method for achieving sensorless position control of hydraulic cylinders driven by direct driven hydraulic units. Direct driven hydraulics is a pump controlled hydraulic system that uses an electric motor driven pumps to drive a single actuator, which brings energy saving and controllability advantages to traditional valve controlled hydraulics. Advantages and disadvantages of various types of hydraulic cylinder position sensors were investigated. These sensors, while accurate, have been noted to be rather expensive and some types have been problematic to implement in some harsh environment applications. Virtual sensors can provide an alternative to physical position sensors. Using only torque and speed data received from electric pump motor controller it is possible to simulate the position of a cylinder provided that all relevant parameters are known. A Sandvik EJC90 mining loader, fitted with diesel electric hybrid drivetrain and direct driven hydraulic units for bucket and boom actuation, was used as a test platform. The hydraulic systems were instrumented with pressure, temperature and cylinder position sensors for research purposes. Simulation of the direct driven hydraulic system was done using Matlab Simulink Simscape hydraulics blocks. Parameters for components were gathered from manufacturer datasheets and those not available are to be measured from the real system. Simulated results of cylinder movement at a motor torque and speed level will be compared to measurements made with the real systems. Preliminary results within the simulation show that the model can reach an accuracy within a few millimeters for a single cycle. A cumulative error for repeated cycles was observed, which recommends simple cylinder end or middle point proximity sensors to be used as reference points.Peer reviewe